a) Field of the Invention
The invention relates to a securement device of an at least height-adjustable steering column, with an openable and closable locking means, which comprises a locking member adjustable via an adjustment path between an open and a closed position, in the open position of which toothings of at least one securement part and at least of one securement counterpart are spaced apart from one another and the height adjustment is enabled and with the adjustment of which from its open position into its closed position the toothings move against the force of at least one spring acting between the securement part and the securement counterpart toward one another in a closure direction and come into engagement with one another.
b) Description of Related Art
Adjustable steering columns are known in different embodiments. In the case of steering columns comprising height adjustment, the height of the steering wheel is adjustable over a certain range, an adjustment of the inclination of the steering column taking place in its section adjoining the steering wheel. Such adjustable steering columns frequently include a length adjustment in addition.
To fix the shell tube housing and supporting the steering spindle in the closed state of the locking means various mechanisms can be employed, for example disk packs acting in the manner of a multiple disk clutch are employed for this purpose. Securement devices are furthermore known which comprise for this purpose securement parts with toothings which can be brought into engagement with one another. The adjustment of the steering column in such securement devices in the open state of the locking means runs extremely smoothly and, in the closed state of the locking means, high holding forces can be applied. Such securement devices with toothed parts engaging one another in the closed state of the securement device are disclosed for example in EP 0 836 981 B1 and EP 0 755 842 B1. To close the locking means a locking member is swivelled, which herein is displaced in the axial direction of a locking bolt, through a connecting link, the link cooperating with the locking member, which has oblique faces, whereupon the locking bolt pulls a securement counterpart having a toothing against a securement part having a toothing. During the opening of the locking member the securement counterpart is raised from the securement part through a spring acting between these two parts, whereby the height adjustment of the steering column is enabled.
Further securement devices, in which for fixing the steering column in the closed state of a locking means toothings of a securement part and of a securement counterpart are brought into engagement with one another, are disclosed inter alia in EP 0 440 403 B1, U.S. Pat. No. 5,787,759 A, EP 0 125 333 B1 and EP 0 139 295 B1. The last two of these documents show so-called “head tilt steering columns” in which the swivel axis for the inclination adjustment of the steering column is located in comparative proximity to the steering wheel. Thereby a relatively large height adjustment range of the steering wheel can be provided. Such head tilt steering columns conventionally comprise a spring, which, with the opening of the locking means, pulls the steering column into its end position in which it is swivelled completely upwardly, whereby the entering and exiting of the driver is facilitated. Problematic is herein that the teeth of the toothings ratchet along one another during the opening of the locking means, in particular if this takes place slowly, through the springs pulling upwardly the part of the steering spindle adjacent to the steering wheel. This leads to an unpleasant noise and to the wear-and-tear of the teeth. This problem may also occur in steering columns without such part of the steering spindle adjacent to the steering wheel or of the spring acting upon the shell tube section supporting the steering spindle, if the height of the steering column is adjusted before the locking means has been completely opened.
With securement devices having toothings the problem may occur that the tips of the teeth of the opposing toothings are directly opposite one another (“tooth-on-tooth position”), when the locking means is to be closed, whereby the securement device cannot be closed correctly but rather first a certain movement of the steering column is required. Various devices have already been proposed by means of which the impacting of the tooth tips when closing the locking means is to be prevented. Such devices are for example described in DE 198 39 496 A1, U.S. Pat. No. 5,787,759 A, DE 39 14 608 C1, EP 0 796 780 A2 and DE 198 46 292.